Method and Device for Subsea Sampling

ABSTRACT

A sampling device is for subsea fluids. The sampling device comprises:
         a sample container including a first chamber and a second chamber, the first and second chambers being isolated by a movable separating body,   a first pressure sensing device for sensing the pressure in the first chamber of the container, and   a second pressure sensing device for sensing the pressure in the second chamber of the container. The sampling device further comprises a pressure compensating device, the pressure compensating device being adapted to compensate for pressure changes in the first chamber of the container by regulating the pressure in the second chamber of the container and thereby moving the separating body.       

     A method is for subsea fluid sampling using a sampling device.

The invention relates to a method for keeping the content of a samplevessel at an essentially constant pressure. More specifically theinvention relates to a method for maintaining the pressure conditions ofa sample taken subsea while transporting the sample away from thelocation where it was taken. The invention also includes a device forpracticing the method.

Cooling of fluids sampled subsea will cause contraction of the fluid andwith the contraction a drop in pressure. The subsequent drop in pressuremay lead to gases entrained within the fluid releasing. Once the gasesare released they cannot be re-dissolved within the liquid. Thereforeprecise laboratory analysis cannot take place.

Devices are known that use pistons to allow evacuation of the samplevessel while keeping the fluid in phase state.

The object of the invention is to remedy or to reduce at least one ofthe disadvantages of the prior art, or at least to provide a usefulalternative to the prior art.

The object is achieved by virtue of features disclosed in the followingdescription and in the subsequent claims.

The overall objective of the invention is to improve the quality oflaboratory analysis of fluid samples taken subsea, primarily in the oil-and gas industry. The sample content may be filled onto a sample vesselby a method and a device known per se, for example as described inNorwegian patent application no. 20110774, with the title “Method anddevice for filling a submerged sample bottle” and filed by the presentapplicant. By keeping the content of the sample vessel at an essentiallyconstant pressure, where the essentially constant pressure may beessentially equal to or higher than the pressure at the location wherethe sample was taken, it is possible to maintain the sample in itsoriginal fluid state and thereby prevent volatile sample content fromvaporizing. The invention thus makes it possible to analyse the subseasamples in their original fluid state in an on-shore or offshorelaboratory facility.

In a first aspect the invention relates to a sampling device for subseafluids, the sampling device comprising:

-   -   a sample container including a first chamber and a second        chamber, the first and second chambers being isolated by a        movable separating body;    -   a first pressure sensing device for sensing the pressure in the        first chamber of the sample container;    -   a second pressure sensing device for sensing the pressure in the        second chamber of the sample container, wherein the sampling        device further comprises a pressure compensating device, the        pressure compensating device being adapted to compensate for        pressure changes in the first chamber of the sample container by        regulating the pressure in the second chamber of the container        and thereby moving the separating body.

By keeping the sample at or above the original sampled pressure, thequality of sample may be maintained. The movable separating body of thesample container may in one embodiment be a piston, floating orconnected to a piston rod. In other embodiments the movable separatingbody may be an elastic diaphragm or a totally enclosed bladder.

The pressure sensing devices, which may be conventional pressure gaugesas known to a person skilled in the art, may sense the pressure directlyin the chambers of the sample container, or indirectly in fluids linesor other devices connected to the two chambers.

In one embodiment the pressure compensating device may comprise anaccumulator. The accumulator may be a compressed inert gas accumulator.The inert gas container may be external to the sample container, or theinert gas container may be integral with the sample container.

The accumulator may be directly connected to the second chamber of thesample container. Alternatively the accumulator may be indirectlyconnected to the second chamber of the sample container by means of anactuator cylinder. A piston rod of the actuator cylinder may bemechanically connected to a separating movable piston in the samplecontainer.

In alternative embodiments the pressure compensating device may comprisea pump or a linear actuator, both in fluid communication with the secondchamber of the sampling device. The pump may be reversible, and thelinear actuator may be mechanic, hydraulic, or pneumatic.

In a second aspect the invention relates to a method for subsea samplingof fluids by means of a sampling device according to the abovedescription, the method comprising the steps of:

-   -   collecting a fluid sample in the first chamber of the sample        container in a subsea environment;    -   moving the sample container from the subsea environment and to        an offshore or on-shore location, wherein the method further        comprises the step:    -   by means of a pressure compensating device to compensate for        pressure changes in the first chamber of the sample container by        regulating the pressure in the second chamber of the sample        container and thereby moving the separating body.

The separating body and the pressure compensating device are used toovercome the large temperature fluctuations seen in the subseaenvironment, samples can be taken at wellhead pressures which can be inexcess of 120° C. The sample container, once removed from the samplepoint, is exposed to sea bed temperatures close to 0° C.

Calculations in line with API 521 show the effect of temperature onfluids to have a significant effect on pressure. The pressurecompensating device according to the invention will make up any pressuredifferential due to temperature changes as will be seen in a subseaenvironment. The pressure compensating device will also act as a safetydevice if the temperature increases. If the sampling device is in dangerof becoming over pressurised by a temperature increase, the pressurecompensating device will allow fluid expansion while keeping thepressure within design parameters. Upon the sampling device then coolingthe pressure compensating device will then maintain pressure so keepinggases entrained.

Hereinafter, an example of a non-limiting, preferred embodiment isdescribed and is depicted on the accompanying drawings, where:

FIG. 1 shows a schematic diagram of a first embodiment of a samplingdevice according to the present invention;

FIG. 2 shows a schematic diagram of a second embodiment of a samplingdevice according to the present invention;

FIG. 3 shows a schematic diagram of a third embodiment of a samplingdevice according to the present invention;

FIG. 4 shows a schematic diagram of a fourth embodiment of a samplingdevice according to the present invention; and

FIG. 5 shows a schematic diagram of a fifth embodiment of a samplingdevice according to the present invention;

In the following the reference numeral 1 indicates a sampling deviceaccording to the present invention. The figures are shown simplified andschematic. Identical reference numerals indicate identical or similarfeatures in the figures.

In FIG. 1 a first sampling device 1 according to the invention is shown.A sample container 11 is divided into a first chamber 111 and a secondchamber 113 by means of a sealingly movable separating body 112 in theform a floating piston. A not shown sample is contained in the firstchamber 111 of the sample container 11. The not shown sample iscollected subsea through sample fluid lines 14 a closable by isolationvalves 12. The pressure of the sample in the first chamber 111 ismeasured by a first pressure gauge 13 a, while the pressure in thesecond chamber 113 is measured by a second pressure gauge 13 b. Thesecond chamber 113 of the sample container 11 is fluidly connected to apressurized inert gas accumulator 15. One side of the accumulator 15contains inert gas supplied via an inert gas line 151 while the otherside of the accumulator is fluidly communicating with a hydraulic fluidcontrol line 153. As the collected sample is moved from the subseaenvironment to an offshore or on-shore laboratory facility, thesurrounding temperature will change and thus change the sample pressure.The first pressure gauge 13 a, which may be s connected to a not showncontrol unit, will sense the varying pressure. The accumulator 15, whichis fluidly communicating with the second chamber 113 of the samplecontainer 11, will then increase the pressure in the second chamber 113,and thus move the sealingly movable floating piston 112 to compensatefor the pressure changes in the first chamber 111, thus maintaining thesample at an essentially constant pressure.

In FIG. 2 a second sampling device 1 according to the invention isshown. A pressurized inert gas accumulator 15 is is connected to thesample container 11 via an actuator cylinder 16. The accumulator 15 isconnected to an inert gas line 151 and to hydraulic control fluid lines154, 155. The actuator cylinder 16 displaces the piston 112 in thesample container 11 by means of a piston rod 166 common to the actuatorcylinder 16 and the sample container 11. The actuator cylinder 16comprises a first chamber 161 and a second chamber 163 separated by apiston 162 also connected to the piston rod 166. The cylinder actuator16 is regulated by pressurizing the first chamber 161 through an openingline 165 or the second chamber 163 through a closing line 164. Thisembodiment of the invention is directly compatible with the previouslymentioned Norwegian patent application no. 20110774.

FIG. 3 shows a third sampling device 1 according to the invention. Anaccumulator 2 is integral to the sample container 11 in that the secondchamber 113 is provided with a pressurized gas cap 19 of inert gases,without any external connections, except from the pressure gauge 13 b.Pressure conditions are maintained within the first chamber 111 of thesample container 11 solely by use of the gas cap 19 contained in thesecond chamber 113 of the sample container 11.

FIG. 4 shows a fourth sampling device 1 according to the invention. Alinear actuator 17, connected to a not shown control unit, is used tosimulate the action of an accumulator, thus to regulate the pressure inthe sample container 11. The linear actuator 17 may be mechanic,hydraulic, or pneumatic.

In FIG. 5 a fifth sampling device 1 according to the invention is shown.A pump 18 is used to simulate the action of an accumulator, thus toregulate the pressure in the sample container 11.

In general the above mentioned processes may be performed manually orautomatically by means of control units communicating with the variouscomponents of the embodiments.

It should also be understood that components of the various embodimentscan be combined to provide additional embodiments also within the scopeof the present invention.

1. A sampling device for subsea fluids, the sampling device comprising:a sample container including a first chamber and a second chamber, thefirst and second chambers being isolated by a movable separating body; afirst pressure sensing device for sensing the pressure in the firstchamber of the sample container; a second pressure sensing device forsensing the pressure in the second chamber of the sample container; anda pressure compensating device, the pressure compensating device beingadapted to compensate for pressure changes in the first chamber of thesample container by regulating the pressure in the second chamber of thecontainer and thereby moving the separating body.
 2. The sampling deviceaccording to claim 1, wherein the pressure compensating device comprisesan accumulator.
 3. The sampling device according to claim 2, wherein theaccumulator is a compressed inert gas accumulator.
 4. The samplingdevice according to claim 2, wherein the accumulator regulates theseparating body in the sample container via an actuator cylinder.
 5. Thesampling device according to claim 1, wherein the pressure compensatingdevice comprises a pump.
 6. The sampling device according to claim 1,wherein the pressure compensating device comprises a linear actuator. 7.A method for subsea sampling of fluids by sampling device comprising: asample container including a first chamber and a second chamber, thefirst and second chambers being isolated by a movable separating body; afirst pressure sensing device for sensing the pressure in the firstchamber of the sample container; a second pressure sensing device forsensing the pressure in the second chamber of the sample container; anda pressure compensating device, the pressure compensating device beingadapted to compensate for pressure changes in the first chamber of thesample container by regulating the pressure in the second chamber of thecontainer and thereby moving the separating body; the method comprising:collecting a fluid sample in the first chamber of the sample containerin a subsea environment; moving the sample container from the subseaenvironment and to an offshore or on-shore locations; and using apressure compensating device to compensate for pressure changes in thefirst chamber of the sample container by regulating the pressure in thesecond chamber of the sample container and thereby moving the movableseparating body.